SPS Adsorption and Desorption during Copper Electrodeposition and Its Impact on PEG Adsorption

The adsorption and activation of bis (3-sulfopropyl)-disulfide (SPS) has been studied using a microfluidic electrochemical device. The device provides for accurate transitioning of solution over the working electrode allowing for addition or removal of additives from a base plating electrolyte. The transition from a plating bath to a polyethylene glycol bath shows a quick suppression of copper deposition similar to that seen with a bath. Acceleration at longer times, presumably by the activation of adsorbed SPS species, is a function of SPS concentration and applied cathodic potential. When copper is plated in the presence of SPS and for times around before the introduction of PEG, the activated SPS appears to inhibit the adsorption of PEG to the surface. System response to chloride ion addition or removal is relatively fast. Desorption of an activated layer occurs slowly, even at high cathodic potentials of , where current densities are over . Numerical simulations show that the time needed for PEG to saturate the bottom of a sub- feature is small relative to SPS activation times.